Global warming caused by emission of greenhouse gases has become a worldwide problem. The greenhouse gas includes carbon dioxide (CO2), methane (CH4), freons (CFCs), etc. Among them, CO2 has the most significant effect on global warming and reduction of CO2 emission is an urgent subject. Methods of separating and recovering CO2 for decreasing the amount of CO2 emissions include, for example, a chemical absorption method, a physical absorption method, a film separation method, a capturing and separation method, and a cryogenic separation method. Further, the method of separating and recovering CO2 includes, for example, a CO2 capturing and separation method using a solid CO2 capturing material.
In a CO2 separation unit using a CO2 capturing material, a gas containing CO2 (CO2-containing gas) is introduced into a capturing material container filled with the CO2 capturing material, and the CO2-containing gas are brought into contact with the CO2 capturing material to capture and remove CO2 by the CO2 capturing material. Subsequently, captured CO2 is desorbed and recovered by heating the CO2 capturing material. An example of the CO2 separation and recovery method is described in Patent Literature 1.
The method of heating the CO2 capturing material to desorb CO2 and regenerate the CO2 capturing material includes a method of bringing a heated gas directly into contact with a CO2 capturing material and heating the material, and a method of indirectly heating the CO2 capturing material by causing a heated gas to flow through a heat conduction pipe. As the heated gas, steam is utilized. However, when steam is used, since energy necessary for separation and recovery of CO2 is increased, the amount of used steam is preferably smaller. The method of decreasing the amount of the used steam includes improvement of the heating method and reutilization of the steam used.
The method of heating the CO2 capturing material includes the techniques described, for example, in Patent Literature 2 and Patent Literature 3. In the technique described in the Patent Literature 2, an adsorption step, a regeneration step and a cooling step are performed successively by rotating a drum-shaped CO2 capturing material using zeolite as a starting material. In this system, the CO2 capturing material is heated during regeneration by a high temperature CO2 circulating to desorb CO2. Further, in the technique described in the Patent Literature 3, after capturing CO2 by using a CO2 capturing material comprising activated carbon with addition of potassium carbonate and sodium carbonate, CO2 is desorbed by direct contact of steam with the CO2 capturing material.